Neuronal correlates of clinical asymmetry in progressive supranuclear palsy

Progressive supranuclear palsy (PSP) is characterized by a symmetric hypokinetic syndrome with early falls and vertical supranuclear gaze palsy. However, clinically asymmetric manifestations occur, resembling idiopathic Parkinson disease or corticobasal degeneration. The aim of this study was to determine the neuronal correlates of patients suffering from PSP with a lateralized disease manifestation (hemi-PSP) in comparison to patients with symmetric clinical presentation (symPSP) and corticobasal degeneration.

Twenty-three patients with PSP and 8 patients with corticobasal degeneration according to standard diagnostic criteria underwent F-fluorodeoxyglucose (FDG) PET scans to assess disease-specific patterns of regional cerebral glucose metabolism reflecting neuronal activity. Group differences were analyzed by statistical parametric mapping and region-of-interest analyses.

Clinically, 14 patients presented with symPSP while 9 patients were considered as hemi-PSP. Patients with symPSP or hemi-PSP showed similar bilateral medial frontal hypometabolism compared to corticobasal degeneration patients. In contrast, corticobasal degeneration patients exhibited a prominent parietal hypometabolism compared to both symPSP and hemi-PSP patients. SymPSP patients showed no significant hypometabolism compared to hemi-PSP, whereas hemi-PSP patients presented with significant hypometabolism of the motor thalamus, middle cingulate gyrus, and sensorimotor cortex contralateral to the most affected body side compared to symPSP patients.

The present study demonstrates that a more pronounced and asymmetric involvement of cortical and subcortical motor areas is associated with a lateralized disease manifestation of PSP. Furthermore, these findings strongly suggest that FDG PET imaging may assist the challenging clinical differentiation between hemi-PSP and corticobasal degeneration by depicting disease-specific patterns of regional cerebral glucose metabolism.